Catalyzed oxygen bleaching

ABSTRACT

A METHOD FOR THE DELIGNIFICATION AND BLEACHING OF LIGNOCELLULOSIC MATERIALS UNDER THE ACTION OF OXYGEN AND ALKALI IN AN ALKALINE MEDIUM AND IN THE PRESENCE OF FROM ABOUT 0.005% TO ABOUT 5.0%, BY WEIGHT, BASED ON THE WEIGHT OF SAID MATERIAL, OF A COPPER-CONTAINING MATERIAL WHICH CONVERTS, AT LEAST IN PART, TO COPPER OXIDE IN THE PRESENCE OF SAID ALKALI IN SAID ALKALINE MEDIUM.

United States Patent 3,736,224 CATALYZED OXYGEN BLEACHING Martin Grayson, Stamford, and Charles Edward Farley, Norwalk, Conn., assignors to American Cyanamid Company, Stamford, Conn. No Drawing. Filed June 16, 1971, Ser. No. 153,679

Int. Cl. D21c 9/10 US. Cl. 16265 12 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The delignification and bleaching of ligno-cellulosic materials has been of prime importance in the paper industry for a great many years. Chlorine bleaching has long been the mainstay in this field, but with the most recent public awareness of preserving natural ecology, the practice of this method has been substantially reduced.

Oxygen bleaching, as represented by US. Pat. No. 3,384,533, has more recently evolved as the commercially practiced method of reducing the lignin, and consequent- 1y increasing the brightness, of ligno-cellulosic materials. By utilizing the patentees bleaching methods for example, pollution of bleach plant efiluents is substantially reduced by permitting cyclic recovery of alkali values.

SUMMARY One of the basic problems of oxygen bleaching procedures now practiced is the fact that expensive pressure vessels are required and high pulp consistencies must be maintained.

As a result of our novel method, very low or even atmospheric pressures can be used in an open vessel thereby obviating the need for expensive equipment. Additionally, our novel method enables the use of low pulp consistencies, i.e. below if desired, coupled with the benefits derived from oxygen bleaching as against bleaching with chlorine. A further advantage of the novel process disclosed herein resides in the fact that physical characteristics, e.g. the molecular weight, as represented by the viscosity of the solution, of the pulp are not significantly lowered or otherwise degraded as might be expected due to the substantial chemical breakdown of cotton when reacted with copper as taught by Michie et al.; Effect of Copper on the Autoxidation of Cellulose Suspended in Sodium Hydroxide Solution; Journal of Polymer Science, Part A, vol. 2; pages 225238; 1964.

DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS As mentioned briefly above, our novel process comprises delignifying and bleaching ligno-cellulosic material utilizing a copper-containing material which converts, at least in part, to copper oxide in the presence of alkali as a catalyst during oxygen bleaching. Cupric and cuprous oxide, of course, may be considered to fall within the scope of this definition of useful materials although, in a strict sense, no conversion thereof takes place during the bleaching procedure.

The copper catalyst may be in the form of a cuprous or cupric compound, complex, association or other configuration and should be employed in amounts ranging from about .005 to about 5.0 weight percent, calculated 3,736,224 Patented May 29, 1973 as copper oxide, based on the Weight of ligno-celluloslc material being treated. Preferably, the catalyst should be employed in amounts ranging from about 0.01 to about 2.0 weight percent, same basis.

The catalyst should be well dispersed throughout the bleaching medium in that better dispersion achieves better results, however, complete dispersion is not a requirement of the instant process and is, therefore, not critical.

By the term copper oxide as used herein, is meant cupric oxide, cuprous oxide or both.

Examples of suitable copper compounds useful herein include copper metal, copper alloys and mixtures of copper with other metals, cupric and cuprous halides such as cupric and cuprous chloride, bromide, iodide etc., cupric and cuprous oxide, cupric and cuprous hydroxide, cuprous and cupric sulfate, nitrate, ammonium nitrate, ammonium pyrophosphate, carbonate etc.; cupric or cuprous sulfide; tetramine cupric sulfate; basic cupric sulfate, i.e. Cu (OH) SO ammono-cupric sulfate complex, i.e. Cu(NH ).,SO 'H O copper salts or complexes of organic acids (chelates) such as malonic acid, succinic acid, naphthenic acid, glutaric acid, phthalic acid, salicylic acid, citric acid, lactic acid, tartaric acid, linoleic acid, malic acid, ascorbic acid and the like; nitrogeneous complexes etc. of copper with for example, pyridine, 2,2'-bipyridine, 2-carboxypyridine, 2,6-dicarboxypyridine, amino acids, 8- hydroxyquinoline, imidazole, histidine, piperidine, morpholine, alkyl and aryl amines etc.; copper complexes of phosphines, e.g. tris(Z-carboxyethyl)phosphine, bis (1- carboxyl-l-hydroxyethyl)phosphinic acid etc.; complexes of dextrose, starch, catechol with copper and the like. Additionally, one may utilize compounds formed by reacting inorganic copper salts such as cupric ammonium nitrate with an organic sulfur-containing acid such as mono and disulfosuccinic acid, sulfochlorsuccinic acid, sulfo-adipic acid, sulfopyrotartaric acid, sulfoglutaric acid, sulfosuberic acid, sulfosebacic acid, sulfomaleic acid, sul fofumaric acid, sulfodimethylsuccinic acid, sulfomalonic acid, the alkyl esters of these sulfocarboxylic acids such as the methyl, ethyl, propyl, butyl, amyl, hexyl, octyl etc. esters and the like. Furthermore, one may use the copper salts etc. of the monoalkyl esters of sulfuric acid such as monobutyl acid sulfate, monoamyl acid sulfate, monolauryl acid sulfate etc.; the alkyl aryl sulfonates such as octyl benzene sulfonate, dodecyl benzene sulfo nate, isopropyl naphthalene sulfonate etc. and the like. The above listing is not meant to be all inclusive but should be construed only as a partial but representative listing of copper-containing materials which may be use ful herein as catalytic agents.

The process of the present invention should be conducted at a temperature ranging from about 50 C. to about 200 C., preferably from about C. to about C. The process is generally conducted at atmospheric pressure but may be effectively carried out slightly above atmospheric pressure, if desired. Subatmospheric pressures may also be employed.

The delignification and bleaching treatment may be conducted over a period of time ranging from about 15 minutes to 12 hours, preferably from about 30 minutes to 5 hours.

The oxygen gas is charged to the bleaching vessel according to our invention at a partial pressure of from about 0.1 p.s.i. to about p.s.i., preferably from about 1.0 p.s.i. to about 55 p.s.i. The flow rate of the oxygen into the delignification and bleaching vessel should be such that the oxygen gas remains near the saturation point thereof in the medium, depending, of course, on the pressure employed, if any. Alternatively, oxygen gas may be sparged into the vessel or vessels with stirring of the medium sufficient to disperse the gas therein.

The process is conducted in an alkali medium having a pH ranging from about to about 14, preferably from about 12 to about 14.

Any art-recognized alkali may be utilized in our novel process with such compounds as sodium hydroxide, sodium carbonate, trisodium phosphate, potassium hydroxide, carbonate etc., mixtures thereof and the like being exemplary. Such materials as calcium oxide and calcium hydroxide, while useful herein, are not preferred because of their tendency towards scale formation during the bleaching and delignification and the resultant need for scale removal, disposal and related problems.

The ligno-cellulosic materials which may be treated according to our invention include kraft pulp (sulfate pulp), sulfite pulp (nuetral or alkaline sulfite), cold soda pulp, mechanical pulps, such as ground wood, and semimechanical and semi-chemical pulps (N.S.S.C.) of hard and soft woods such as spruce, fir, hemlock, pine, cottonwood, aspen, poplar, oak, maple, cherry, cedar, etc. bamboo, kenaf, coconut hulks, straw, hemp, jute, fiaxseed and the like.

The order of addition of the reagents catalyst, pulp etc. is not critical. It is preferred, however, to add the pulp and some alkali to the aqueous media so as to create a pH thereof of about 610 and then add the copper-containing catalytic material and more alkali to regulate the pH within the range set forth above. The alkali may, however, be added in one slug or in increments during the actual bleaching and delignification of the pulp.

The consistency of the pulp capable of being treated according to our novel process is within the range known to those skilled in the art but is generally lower than most commercially practiced oxygen bleaching procedures. That is to say, the consistency of the pulp may range from about 0.5% to about 30.0%, by weight, in water, preferably, from about 1.0% to about 10.0%, by Weight.

According to our novel process, after delignification and bleaching are substantially complete, the alkali utilized may be continuously recycled, after removal from the media, back to the delignification and bleaching vessel for ftnlher use. From time to time the alkali may be regenerated, such as by burning etc., between the time it is removed from the bleached pulp and recharged to the delignification and bleaching vessel. Various other organic residues resulting from the delignification and bleaching treatment can also be recycled after periodic purification or regeneration.

The copper-containing material originally added and copper oxides and hydroxides subsequently formed are removed from the reaction media by adding any material thereto which reacts with or associates with the copper materials, oxides and hydroxides to solubilize them and render them removable from the pulp. The copper removal can be effected immediately after the oxygen bleaching or anytime subsequent thereto since more but less severe bleaching steps are usually necessary. The copper material, however, must be totally removed, either in one step or in a plurality of steps, before the pulp is recovered for ultimate use. Additives which react with or associate with the copper materials are added in sufficient quantity after bleaching to solubilize the copper remaining in the bleached pulp and enable recovery thereof. Examples of suitable additives useful for this purpose are sulfuric acid, ammonia, hydrochloric acid, nitric acid, hydrobromic acid, sulfurous acid, sulfonic acid, phosphonic acid, acetic acid, other organic acids, complexing agents such as organic amines, i.e. ethylene diamine, methyl amine, pyridine, 2,2-bipyridyl etc. Generally, for recovery purposes, any agent which reacts, joins, associates etc. with the copper to reform any of the copper materials mentioned above back to their original soluble state may be used to remove the copper from the reaction media.

Our novel process can be conducted as the sole delignification and bleaching treatment of the ligno-cellulosic material prior to its use in forming ultimate consumer products or it may be used in conjunction with one or more other known bleaching treatments. For instance, previous to or, preferably, subsequent to our novel delignification and bleaching treatment, chlorine bleaching, chlorine dioxide bleaching, hypochlorite bleaching etc. can also be carried out on the previously bleached pulp. This is especially effective in chlorine bleaching because chlorine pollution is more of a problem in the initial bleaching of pulp than it is in the bleaching or partially or substantially bleached and delignified pulp.

Furthermore, our novel process can be carried out during a conventional oxygen pulping operation whereby wood chips, for example, are converted to pulp under known conditions and simultaneously delignified and bleached according to our process by the addition of the copper material catalyst to the pulping vessel.

Prior to bleaching and delignification according to our novel process, any known treatment may be conducted on the pulp media such as sulfur dioxide, sulfuric acid washing etc. Additionally, bleaching promoters such as hydrogen peroxide, t-butyl hydrogen peroxide, peracids etc. or materials which generate peroxides in situ during oxygen bleaching may be added before or during our novel process and subsequently recovered and/or recycled for further use. Similarly, various stabilizers known to those skilled in the art to prevent the degradation of cellulose such as magnesium salts, silicates, titanium dioxide etc. may be added to the pulp solution before or during treatment according to the instant invention in amounts similarly well known.

The delignifified and bleached pulp recovered after our novel process may be utilized to form printing papers, newsprint paper, molded products, corrugated paper, box boards, or any product conventionally prepared from bleached pulp.

The following examples are set forth for purposes of illustration only and are not to be construed as limitations on the present invention except as set forth in the appended claims. All parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 In a suitable vessel, 6.0 parts of an oven dry pulp of mixed Northern softwood species are treated fifteen minutes with 1000 parts of 0.01 N sulfuric acid, filtered and reslurried in 500 parts of distilled water. To the resultant slurry is addded 0.25 weight percent, based on 0D. pulp, of copper sulfate with agitation. 15.3 parts of sodium hydroxide in 700 parts of water are then added, resulting in a final alkali level of 0.317 M and a pulp consistency of 0.5%. Oxygen is introduced into the slurry through a gas dispersion tube. A stainless steel steam coil is utilized to heat the vessel to C. and this temperature is maintained for 2 hours, after which time the pulp slurry is filtered, reslurried several times in distilled water and finally slurried in 0.01 N sulfuric acid for 5 minutes to solubilize the deposited copper oxide as sulfate.

A handsheet is then made from the bleached pulp in the conventional manner. The brightness thereof is determined to be 50.1.

When the same procedure was followed on a second portion of the same master batch of pulp but omitting the copper sulfate catalyst addition, all other procedures remaining constant, the resultant handsheet had a brightness determined to be 38.2.

Following the procedure of Example 1 a series of different copper-containing materials are substituted for the cupric sulfate thereof. A different wood pulp is utilized as indicated by Example 2. The results are set forth in the following Table I.

TABLE I E Sheet brightness x. No. Copper material I 1 hour 2 hours 3 hours 48. 2 51. 3 53. C 51. 7 56. 4 57. 7 4- Cu-2,2-bipyridine 52. 5 56. 6 59. 7 5- Cupric salicylate 51. 6 53. 8 57. 2 6- Cupric citrate d 52. 7 55. 6 59. 4 7- Cupric-l-oarboxy-l-hydroxyethyl 48. 7 53. 9 56. 4

phosphinate.

8. Cupric-8-hydroxy quinolinatek-.- 49. 3 54. 1 56. 7 9- CuCl 53.1 56.7 60.6 52. 9 55. 3 59. 8 49. 7 52. 9 58. 1

0.1 mmoles Cu /6 g. pulp unless indicated otherwise. b Comparison.

Cu /ligand ratio 1:2.

d Cu /figand ratio 1:1.

EXAMPLE 12 Six parts of a hardwood kraft pulp with an initial brightness of 26.6 is stirred for 30 minutes in 500 parts of aqueous sulfur dioxide at a pH of 2.0. The liquid is removed by filtration. The pulp is then suspended in 1200 parts of water containing .013 part of cupric chloride, and 4.8 parts of sodium hydroxide are then added. The mixture is heated in a suitable glass cylinder using an internal steam coil and is maintained at 951-1 C. Oxygen gas is bubbled into the bottom of the open vessel. The gas bubbles stirring the mixture gently. After three hours the treatment is halted and the pulp is recovered by filtration. The treated pulp is stirred for minutes in 500 parts of 0.2% sulfuric acid and then dried. The bleached pulp has a brightness of 58.7.

Pulp treated similarly, but with the cupric chloride omitted, has a brightness of 52.4.

EXAMPLE 13 The procedure of Example 12 is again followed but with .010 part of cuprous chloride substituted for the cupric chloride. The bleached pulp has a brightness of 59.4.

EXAMPLE 14 The procedure of Example 12 is again followed, but with .025 part of copper citrate substituted for the cupric chloride. The bleached pulp has a brightness of 59.3.

EXAMPLE 15 Forty parts of hardwood kraft pulp with a brightness of 26.6 is placed in a cylindrical glass reactor equipped with a mechanical stirrer. 1000 parts of water, four parts of sodium hydroxide, and .100 part of cupric sulfate are added. The resultant mixture is heated with stirring and maintained at 95 i1 C. Oxygen gas is passed slowly over the surface of the stirred mixture. An outlet bubbler maintains a pressure of 5 p.s.i.g. (5 lbs. above atmospheric pressure) in the reactor. After 2 hours, the treatment is halted and the pulp is separated by filtration. The bleached pulp is stirred for 15 minutes in 2000 parts of 0.01% sulfuric acid and then filtered, washed with water and dried. The bleached pulp has a brightness of 54.3.

Pulp treated similarly, but with the cupric sulfate omitted, has a brightness of 49.0.

EXAMPLE 16 Six parts of a bisnlfite pulp (initial brightness 50.1), 4 parts of sodium hydroxide, .013 part of cupric chloride, and 1000 parts of water are charged to a cylindrical glass reactor. Oxygen gas is bubbled through the mixture for one hour. The acid washing procedure of Example 1 is then followed. The recovered bleached pulp has a brightness of 74.6.

Pulp treated similarly, but with the culpric chloride omitted, has a brightness of 69.0.

EXAMPLE 17 Carrying out the same procedures as in Example 17 above at a temperature of 99 C. gives a pulp yield of 71.5% in the absence of CUSO and 42% with the copper catalyst present. The respective kappa numbers are 91.1 and 42.5, respectively.

Following the procedure of Examples 12 and 17, various copper-containing materials are substituted for the cupric chloride and cupric sulfate thereof. The results are set forth in Table II, below.

TABLE II Followed procedure Ex. of Example Bright- Kappa No. Copper-contamingmaterial No. ness No.

19- Cuprous nitrate 20. Basic cnpn'c sulfate 21. Cll(NHa)4SO4IHzO 22- Oupric suecinate. 23 Cuprous tartate 24- Cupric imidazolate 12 58. 1 25. Cupric morpholine complex 12 57. 5 26. Copper-starch complex 17 67 27 Oupric disulfosuceinate. 12 58. 3 28. Cuprous sulfoglntarate 12 59. 1 29. Cuprous dodecyl benzene sulfonate 17 71 We claim:

1. A method which comprises delignifying and bleaching ligno-cellulosic material under the action of oxyen and alkali in an alkaline medium and in the presence of from about 0.005% to about 5.0%, by weight, based on the weight of said material, of a copper-containing material which converts, at least in part, to copper oxide in the presence of said alkali in said alkaline medium.

2. A method according to claim 1 wherein said coppercontaining material is cupric sulfate.

3. A method according to claim 1 wherein the delignifying and bleaching is conducted at a temperature of from about 50 C. to about 200 C.

4. A method according to claim 1 wherein the delignifying and bleaching is conducted at atmospheric pressure.

5. A method according to claim 1 wherein the delignifying and bleaching is conducted at a pH ranging from about 10 to about 14.

6. A method according to claim 1 wherein said copper-containing material is cupric chloride.

7. A method according to claim 1 wherein said c0pper-containing material is cuprous chloride.

8. A method according to claim 1 wherein the copper oxide formed is removed from the bleached and delignified material.

9. A method according to claim 1 wherein the coppercontaining material is an organic copper complex.

10. A method according to claim 1 wherein the copper-containing material is a copper salt of an organic acid.

1 1. A method according to claim 1 wherein the coppercontaining material is copper oxide.

7 8 12. A method according to claim 1 wherein the cop- OTHER REFERENCES I per-containing material is copper hydroxide. Rydholm, pulping Processes, 1049, (GR 173).

References Cited 8. LEON BASHORE, Primary Examiner UNITED STATES PATENTS 5 A. L. CORBIN, Assistant Examiner 2,511,096 6/1950 Bate 162-65 3,657,065 4/1972 Smith et a1. 162-65 2,477,631 8/1949 Levy et a1. 162-79 X 8 111; 

